Various different techniques have been used in an attempt to flow air through a contained space of a system including air distribution systems for conditioning the temperature of the air and the rate of such air flow being in related to the static pressure in the system. The rate of airflow through the air distribution systems also affected by the speed and torque of a motor used in the system.
One approach involves the laborious task of matching the motor speed and torque with the proper fan to approximate the desired air flow rate for a particular contained space and static pressure of a particular air distribution system. However, this does not accommodate variations in the static pressure in the air distribution system caused by alterations in the system such as the opening, closing or adjusting of a damper connecting a conditioned space in air flow relation with the system. In addition, other devices, such as filter and heat exchangers, may alter the static pressure within the duct system.
If the fan or blower utilised in such systems is of the fan or blade type, an increase in the static pressure acting on such fan will result in a decrease in the air flow rate.
Another approach has been to compensate for the alteration in the speed of fans and the electric motors by employing an apparatus for controlling the motor speed, which requires the calculation of constants specific for each apparatus and air distribution system combination. This apparatus includes a controller, which drives the motor at various speeds but cannot be used with a general motor controller.
It is an object of the present invention to provide an improved system for conditioning air and for maintaining a preselected air flow rate of the conditioned air through at least part of the system regardless of the static pressure therein.